Engine antifreeze composition

ABSTRACT

In general this invention relates to an antifreeze composition that can be used in the cooling systems of internal combustion engines, for example, in heavy-duty diesel engines, light duty trucks and cars. The antifreeze composition can be added to water or other suitable liquid coolant in the cooling system, to lower the freezing point temperature of the coolant and inhibit corrosion of metallic components associated with the cooling system. The antifreeze composition is particularly well suited, although not exclusively, for use with hard water. The antifreeze composition includes an organic acid component comprising adipic acid and at least one of benzoic acid and one or more C 9 -C 12  dicarboxylic acid—or salts of these acids. The antifreeze composition also includes other anti-corrosive additive, for example, molybdate, nitrite, nitrate silicate azoles and a variety of buffer agents.

FIELD OF THE INVENTION

In general, this invention is related to a coolant composition. Morespecifically, but not exclusive, this invention is directed to a coolantcomposition that includes anti-corrosion additives for use in combustionengines and a method of inhibiting the corrosion of components incooling systems.

BACKGROUND OF THE INVENTION

Typically coolant compositions are specifically formulated with ethyleneglycol or propylene glycol or their derivatives and include specificadditives that inhibit and reduce corrosion of coolant systems. Specificcoolant formulations are desired because with the advent of higherperformance engines, particularly heavy-duty diesel engines, increasingmore components of these engines are manufactured from a wide variety ofmaterials to reduce weight and increase efficiency. Similarly, thecoolant coursing through these engines contact a variety of materials.Typically additives are selected to impart particular benefits, such asproviding protection for one or more selected materials. In addition, itis not uncommon for the additives to be selected to compliment eachother's beneficial properties. Despite the specificity which thesecoolant compositions are formulated, the benefits associated with manyof the additives can be thwarted because a large percentage of operatorsinclude hard water in the cooling system. The hard water can be addedeither upon initially filling the cooling system or during in-service asoperators add make-up water to top off the cooling system.

In many parts of the world, there is no ready access to suitable waterfor use in cooling system. Hard water includes a number of minerals,most notably calcium, magnesium and iron salts. These minerals maycontribute to loss of efficacy and reduce the usable lifetime of thecoolant composition. This loss can be particularly detrimental to heavyduty diesel trucks that can cover over 10,000 miles a month. Anineffective coolant composition can shorten engine life, allow internalpassageways in the cooling system to clog, contribute to cylinder linerpitting and water pump cavitation all which result in costly engineoverhauls.

Thus in light of the above described problems, there is a continuingneed for advancements in the coolant compositions and improved methodsfor reducing corrosion associated with cooling compositions. The presentinvention is such an advancement and provides a wide variety of benefitsand advantages.

SUMMARY OF THE INVENTION

The present invention relates to novel coolant compositions, themanufacture and use thereof. Various aspects of the invention are novel,nonobvious, and provide various advantages. While the actual nature ofthe invention covered herein can only be determined with reference tothe claims appended hereto, certain forms and features, which arecharacteristic of the preferred embodiments disclosed herein, aredescribed briefly as follows.

In one form the present invention provides an engine coolant compositionthat can be used in a cooling system. The engine coolant compositioncomprises: an organic acid component or salt thereof. The organic acidcomponent can include a C₄-C₆ dicarboxylic acid and at least one ofbenzoic acid and a C₉-C₁₂ aliphatic dicarboxylic acid. The enginecoolant also comprises an anticorrosion additive including molybdate,and at least one of mercaptobenzothiazole, benzotriazole, tolyltriazole,nitrite, nitrate, and silicate; a buffer component comprising a sodiumsalt of at least one of a borate salt, and/or a phosphate salt and afreezing point depressant. In one embodiment the organic acid componentof the coolant composition includes adipic acid, benzoic acid andoptionally a C₉-C₁₂ aliphatic dicarboxylic acid. In other embodimentsthe coolant composition includes molybdate, nitrite, nitrate and atleast one of mercaptobenzothiazole or tolytriazole and a bufferingagent.

In another form the invention provides an engine coolant compositioncomprising an organic acid component or salt thereof. The organic acidcomponent can include adipic acid and at least one of benzoic acid and aC₉-C₁₂ aliphatic dicarboxylic acid or salts of these acids; ananticorrosion additive including molybdate, and at least one ofmercaptobenzothiazole, benzotriazole, tolyltriazole, nitrite, nitrate,and silicate; a buffer component comprising at least one of a boratesalt or a phosphate salt and hard water.

In still yet another form the present invention provides a method ofreducing the corrosion of metal surfaces in a cooling system having arecirculating liquid coolant comprising hard water. The method comprisesadding an additive to the liquid coolant. The additive can include anorganic acid component or salt thereof, a anti-corrosion additive and abuffer agent. The acid component can comprise a mixture of a C₄-C₆dicarboxylic acid and at least one of benzoic acid or a C₉-C₁₂ aliphaticdicarboxylic acid. The anti-corrosion additive can include molybdate,and at least one compound selected from the group consisting of:mercaptobenzothiazole, benzotriazole, tolyltriazole, nitrite, nitrate,and silicate.

Further objects, features, aspects, forms, advantages and benefits shallbecome apparent from the description and drawings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanned image of two aluminum coupons after evaluation indifferent engine antifreeze compositions according to the ErosionCorrosion Bench Test.

FIG. 2 is a scanned image of an alternate view of the coupons depictedin FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustratedherein and specific language will be used to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described processes, systems or devices, and any furtherapplications of the principles of the invention as described herein, arecontemplated as would normally occur to one skilled in the art to whichthe invention relates.

In general, this invention is directed to an engine coolant compositionfor heavy duty diesel engines, light duty trucks and automobiles. Thisinvention can also provide various other advantageous applications, forexample, in any heat-transfer application, preferably using anaqueous-based or alcohol-based (including glycols) or otherwisecompatible heat-transfer medium. The coolant composition providesexcellent antifreeze capabilities and therefore lowers the temperatureat which the engine coolant begins to solidify or freeze. In preferredembodiments, this invention includes an organic acid component of aC₄-C₆ dicarboxylic acid and at least one other organic acid incombination with other anti-corrosion additives and buffering agents toreduce corrosion of metal components and clogging of internal systempassageways. It has been determined that certain preferred embodimentsunexpectedly exhibit enhanced anti-corrosion properties in the presenceof hard water.

The term “hard water” when used in this present application isunderstood as water that includes a variety of minerals or inorganicsalts, particularly cationic alkali metal salts, for example, calciumsalts, magnesium salts, iron salts. Hard water can typically beevaluated in terms of its hardness level, which is often reported inparts per million (ppm). Hardness can be determined using a variety ofcommercially available water test kits, for example, using a test kitsold under the trademark Monitor C™ by Fleetguard, Inc. Water isconsidered to be hard at a hardness level of about 170 ppm or greaterand very hard at a hardness level of about 300 ppm or greater.

In preferred formulations, the engine coolant composition of the presentinvention includes a specifically tailored combination of organic acids,anti-corrosion agents and buffering agents to reduce the corrosionassociated with hard water. This can provide an added benefit ofallowing a lower concentration of selected agents to yield equallyeffective anti-corrosion protection. The present invention provides anenhanced benefit of reducing precipitation of salts associated with theuse of hard water in coolant systems.

The cooling composition can be provided as a liquid concentrate or as aready-to-use formulation, i.e., a pre-diluted formulation. Theready-to-use formulation can be used “as is” in a cooling system. Morepreferably the ready-to-use formulation is diluted with water at adilution ratio, by volume, of about 1 part formulation to 0.4 partswater to about 1 part formulation to about 1.6 parts water.

The engine coolant composition of the present invention includes anorganic acid component and other anti-corrosive additives. It should beunderstood that the organic acids impart significant anti-corrosiveproperties, as well as other beneficial properties. The organic acidcomponent consists essentially of a C₄-C₆ aliphatic dicarboxylic acidand at least one of an aromatic carboxylic acid and a C₉-C₁₂dicarboxylic acid or salts of these acids. The anti-corrosive additivescan be a combination of inorganic and organic agents.

Specific examples the C₄-C₆ aliphatic dicarboxylic acid for use in thepresent invention include maleic acid, succinic acid, and adipic acid.In a more preferred form, the organic acid component includes adipicacid. The C₄-C₆ aliphatic dicarboxylic acid is included in the coolantcomposition in an amount sufficient to inhibit corrosion of metalsurfaces in the cooling system. Preferably the coolant compositionincludes the C₄-C₆ aliphatic dicarboxylic acid in an amount betweenabout 0.1 weight percent (wt %) and about 5 wt % measured as the freeacid and based upon the total weight of the coolant composition. Morepreferably, the coolant composition includes between about 0.1 wt % andabout 1 wt % of adipic acid; still yet more preferably, the coolantcomposition includes between about 0.1 wt % and about 0.5 wt % of theadipic acid. It has been unexpectedly determined that when the coolantcomposition includes the minor amount of adipic acid, the coolantcomposition exhibits significantly enhanced anti-corrosive properties,particularly when the coolant composition is combined with hard water.

The organic acid component can also include an aromatic carboxylic acid.Preferably the aromatic carboxylic acid is selected to include benzoicacid or a salt thereof. The coolant composition includes the aromaticcarboxylic acid in varying amounts. When the coolant composition isprovided in a ready-to-use formulation, the coolant includes betweenabout 0.1 wt % and about 5 wt % benzoic acid or benzoate measured as thefree acid and based upon the total weight of the coolant composition.More preferably, the coolant composition includes between about 0.5 wt %and about 2.5 wt % benzoic acid or benzoate; still yet more preferablythe coolant composition includes between about 0.6 wt % and about 1.5 wt% benzoic acid or benzoate.

The organic acid component can also include a C₉-C₁₂ dicarboxylic acid.Preferably the C₉-C₁₂ dicarboxylic acid is selected to include azelaicacid, sebacic acid, undecanedioic acid and dodecanedioic acid or saltsof these acids. The coolant composition includes the C₉-C₁₂ dicarboxylicacid in varying amounts. When the coolant composition is provided in aready-to-use formulation, the coolant includes between about 0.1 wt %and about 5 wt % C₉-C₁₂ dicarboxylic acid or salt thereof measured asthe free acid and based upon the total weight of the coolantcomposition. More preferably, the coolant composition includes betweenabout 0.5 wt % and about 2.5 wt % of a C₉-C₁₂ dicarboxylic acid or saltthereof; still yet more preferably the coolant composition includesbetween about 1.0 wt % and about 2.0 wt % C₉-C₁₂ dicarboxylic acid orsalt thereof. In alternative embodiments of this invention, the coolantcomposition can include between about 2.0 wt % and about 3.0 wt % of theC₉-C₁₂ dicarboxylic acid or salt thereof.

The salts of these acids are preferably, but not exclusively, ammonium,tetraalkyl ammonium and alkali metal salts and would include, forexample, lithium, sodium and potassium cations. Although it isunderstood that sodium and potassium salts are more preferred.

The coolant composition of the present invention also includesadditional anti-corrosive additives. The anti-corrosive additives can beeither an organic additive or an inorganic additive. Examples of organicanti-corrosive additives include benzotriazole, tolytriazole,mercaptobenzothiazole, sulfonates and imidazolines. Preferably thecoolant composition of the present invention includes tolytriazoleand/or mercaptobenzothiazole. The organic anti-corrosive additives canbe included in varying amounts, preferably between about 0.05 wt % andabout 0.5 wt %. More preferably, the coolant composition includesbetween about 0.1 wt % and about 0.5 wt % of the individual organicanti-corrosive additives.

The coolant composition can also include inorganic anti-corrosiveadditives. The inorganic additives include borates, phosphate silicates,nitrates, nitrites and molybdates. These inorganic anti-corrosiveadditives can be employed at concentrations ranging between about 0.0 wt% and about 5.0 wt % for the ready-to-use formulation. The inorganicanti-corrosive additives can be provided as salts, preferably ammonium,tetraalkyl ammonium, or alkali metal salts. In preferred forms thecoolant composition includes two or more of the inorganic anti-corrosiveadditives.

In preferred forms, the coolant composition includes molybdate and atleast one anti-corrosive additive selected from the group consisting ofmercaptobenzothiazole, benzotriazole, tolytriazole, a silicate salt, anitrite salt and a nitrate salt. The basic coolant composition can betailored for selective applications to provide enhanced aluminumprotection for components of the coolant system, for example, nitratesand silicates are known to provide aluminum protection. Borates andnitrites can be added for ferrous metal protection, and benzotriazoleand tolytriazole can be added for copper and brass protection.Furthermore, for heavy-duty specifications, the coolant composition caninclude varying amounts of an alkali metal nitrite to provide enhancedprotection against pitting of cylinder liners for heavy-duty dieselengines. The coolant composition can include between about 0.0 wt % toabout 0.5 wt % of each of the desired additives. More preferably, thecoolant composition can include between about 0.05 wt % to about 0.5 wt% of the additives; still yet more preferably between about 0.1 wt % toabout 0.5 wt % of the additives.

The coolant composition can also include buffering agents. The bufferingagents can be selected from any known or commonly used buffering agents.It will be appreciated by those skilled in the art that selectedbuffering agents can exhibit both anti-corrosion and bufferingproperties. For example benzoate, borates and phosphates can in certainformulations provide both buffering and anti-corrosion advantages.Preferred examples of buffers include borate salts and phosphate salts.In one preferred form, the buffering system includes a mixedphosphate/borate buffer system. It will also be understood by thoseskilled in the art that certain engine manufacturers, governmentalorganizations and/or consumers prefer or even require selected bufferingsystems. While the choice of a selected buffer system is not criticalfor the practice of this invention the buffering agents(s) can beselected to comply with desires and demands of end users. In addition abase can be included into the coolant composition to help adjust the pHto the desired pH level. Illustrative examples of bases for use withthis invention included commonly known and used bases, for example,inorganic bases including KOH, NaOH, and weaker bases such as NaHCO₃.K2CO_(3a) and Na₂CO₃. Therefore, the buffering system and base can beadapted to provide a coolant composition having a pH level between 7.5and about 11 pH units. More preferably, the buffering system and base isselected to provide a coolant composition with a pH level between about8.0 and about 9.0 pH units.

A fully formulated coolant typically includes a variety of otheradditives, including, for example, defoamers, scale inhibitors,surfactants, detergents, and dyes. Specific examples of defoamersinclude components (alone or in combination) such as silicon defoamers,alcohols such as polyethoxylated glycol, polypropoxylated glycol oracetylenic glycols. Examples of scale inhibitors include components,either alone or in combination, such as, for example, phosphate esters,phosphino carboxylate, polyacrylates, polymethacylate, styrene-maleicanhydride, sulfonates, maleic anhydride co-polymer, acrylate-sulfonateco-polymer and the like. Surfactants for use in this invention include,for example, either alone or in combination: Alkyl sulfonates, acrylsulfonates, phosphate esters, sulfosuccinate, acetylenic glycol, andethoxylated alcohols. Detergents include non-ionic and/or anioniccomponents such as, for example, phosphate ester surfactants, sodiumalkyl sulfonates, sodium aryl sulfonates, sodium alkyl aryl sulfonates,linear alkyl benzene sulfonates, alkylphenols, ethoxylated alcohols,carboxylic esters, and the like.

The coolant composition of the present invention is blended to provide auniform composition. The order of addition of the individual componentsis not critical for the practice of the invention. However, it isdesired to the coolant composition be thoroughly blended and that allthe components be completely dissolved to provide optimum performance.As discussed above, in one preferred form, the coolant composition isprovided as a ready-to-use, i.e. pre-diluted, formulation. When thusprovided, the ready-to-use formulation can also include a freezing pointdepressant. The freezing point depressant can be selected from a varietyof known and/or commonly used freezing point depressants. Commonly usedexamples include, for example, propanol, monoethylene glycol, diethyleneglycol, propylene glycol, and the like. When provided in the coolantcomposition, the freezing point depressant is added in amounts rangingbetween about 30 wt % and about 70 wt % based upon the total weight ofthe coolant composition. The ready-to-use coolant composition can alsoinclude varying amounts of water.

In another form, the coolant composition of the present invention can beprovided as a liquid concentrate. Typically, the liquid concentrateincludes an alcohol or glycol and additionally can, but is not required,to include small amounts of water to dissolve the additives. The liquidconcentrate can be added to a cooling system and diluted with water toprovide a liquid coolant. To provide optimum performance, the liquidconcentrate should be thoroughly blended with the water prior to use. Itis preferable, but not required, to pre-mix the concentrate with thecoolant before adding to the coolant system rather than using theradiator as a mixing chamber.

The coolant composition that includes adipic acid provides enhancedanti-corrosion properties over compositions lacking either one of theseacids or salts of these acids. The cooling composition provides enhancedaluminum and ferrous metal protection against corrosion of the coolantin the cooling system.

The cooling composition of the present invention provides unexpectedresults or enhanced protection in hard water. It is not uncommon forcooling system for diesel engines and automobile engines to includewater as part of the coolant medium. Furthermore, during operation, thecooling systems frequently lose fluid either due to leakage orevaporation. Often, operators add make-up fluids such as water to thecooling system. The make-up fluid frequently is hard water, which isfound in many parts of the world. Hard water can cause many deleteriouseffects on the components of the cooling systems. These effects includeincreased corrosion of metal surfaces, particularly iron and aluminumsurfaces. Furthermore, the hard water can cause incompatibility problemswith some of the anti-corrosion components. For example, hard watercontaining calcium and magnesium salts can cause additives toprecipitate or gel. This can decrease engine protection and increasecorrosion. In a typical on-highway heavy-duty diesel engine coolingsystem, the flow rate can range from 80 to 150 gallons per minute. Thismeans that flow velocities can reach 8 to 10 feet per second. Tests haveshown that solder and aluminum are sensitive to the effects of high flowrate. These effects are acerbated by the addition of any solid or gelledadditives.

It has unexpectedly been determined that the addition of adipic acidsignificantly enhances the protection of aluminum components in contactwith hard water. For example, if additives, such as silicates,precipitate from the coolant composition, the desired aluminumprotection previously afforded by the soluble silicate is drasticallyreduced. While not to be bound by any theory, it is thought that adipicacid and its salts provide significant enhanced aluminum metalprotection, and at least part of this effect may be attributed toreduced precipitation of certain additives.

While not to be considered limiting in any fashion, it is also thoughtthat the addition of adipic acid to the cooling composition providesenhanced protection for metal surfaces by chelating or combining withthe alkali metal cations, specifically calcium and magnesium. Thesecations contribute to the buildup of scale on hot metal surfaces. Thescale can drastically reduce and even eliminate flow through passagewaysin the cooling system. The scale can also inhibit efficient heattransfer from the hot metal surfaces to the coolant. Chelation of thesecations can help reduce scale formation on hot surfaces andsignificantly reduces the detrimental effects of scale buildup.

It has been observed that adipic acid in hard water can also provide athin surface coating on many metal components, particularly aluminumcomponents of the cooling system. This coating can range up to severalangstroms thick. While not considered to be limiting in any fashion, itis thought that this coating protects the metal surface from corrosionbut does not appreciably affect heat transfer.

In addition to providing make-up water for in-use cooling systems,frequently operators will add supplemental cooling additives to theircooling systems. Typically, the supplemental cooling additives include avariety of anti-corrosion agents as specified above. It is not uncommonfor an operator to “overdose” selected components of the anti-corrosiveadditive. In particular, it has been noted that nitrite levels inover-the-road diesel engine cooling systems have been increased tolevels that can be detrimental to the aluminum and solder components ofthe cooling systems. The present invention provides enhanced protectionfor aluminum surfaces, thereby ameliorating some of the effects ofover-dosing. It has also been determined that molybdate and the organicdiacids provide ferrous and cylinder lining protection. Because theanti-corrosion properties are enhanced, the concentration of selectedadditives, for example, nitrite salts, can be reduced. This reduces thelikelihood that an operator will overdose the cooling system withnitrite.

For the purpose of promoting further understanding and appreciation ofthe present invention and its advantages, the following Example isprovided. It will be understood, however, that these Examples areillustrative and not limiting in any fashion.

EXAMPLE

Five coolant compositions listed as Examples 1-5 in Table 1 wereprepared by combining the specific indicated components listed in thetable in a fully formulated base antifreeze solution that included, inpercent by weight based on the final total weight of the finalantifreeze formulation, 95% ethylene glycol, sodium borate (0.20%);sodium molybdate (0.30%); mercaptobenzothiazole (MBT) (0.40%, 50%active); tolyltriazole (0.20%); sodium silicate (0.10%) as well assurfactants, scale inhibitors and defoamers (0.05%) to provide aconcentrated coolant composition. Each of the concentrated coolantcompositions was then diluted with water having a hardness of about 300ppm and a pH between about 8.3 and about 8.5 to provide the coolantcompositions listed as examples 1-5. These coolant compositions werethen evaluated according to ASTM D-2809 Standard Text Method forCavitation Corrosion and Corrosion and Erosion-Corrosion Bench Testdescribed below. TABLE 1* Concentrated Coolant Compositions Exam- Exam-Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 Components Adipic acid1.0% — — 0.20% 0.20% Sebacic acid — 1.00% — — — Dodecanedioic — — 1.0%1.4% 1.4% acid NaNO₂(Nitrite) 0.36% 0.36% 0.36% 0.36% 0.20% TestProcedure ASTM D-2809 6 7 7-8 7 8 Erosion 0.4 mg 12.4 mg 87 mg 4.8 mg4.9 mg Corrosion Bench Test*Examples 1-5 were diluted 50:50 with water having a hardness of 300 ppmfor both test procedures.

Erosion Corrosion Bench Test Procedure

This test procedure can help evaluate the effect of high flow velocitieson solder and aluminum components. A fixture containing three preweighedbundles were placed in line of a flowing system. The flow rate andtemperature were held constant throughout the test. The aluminumspecimens were galvanically coupled to cast iron. The test duration wasseven days. At the end of test, the weight loss due to erosion corrosionwas determined on the aluminum samples. The flow stand had a loopcapable of flowing 15 gallons (57 liters) of test solution at 5-50 gal.per minute (19-190) liters per minute), and holding 3 sets of testbundles ( 1 5/8 in. (5.1 cm) diameter radiator hose). Test fixture wascapable of holding 3 sets of test bundles (17 in. (43 cm) length).

A. Specimens and Test Solution Preparation:

Specimens: Aluminum and Cast Iron samples are of the type used in ASTMD-1384 glassware test. Various aluminum alloys for testing can beobtained from Metal Samples Co., Inc. Munford, Ala. The samples werecleaned before testing by placing them in acetone to remove processingoils. The samples were then wrapped in an absorbent towel and placed indessicator to dry. Test solutions were prepared by combining antifreezeand SCA formulations in 300 ppm hard water. The hard water contained 277mg CaCl₂, 123 mg MgSO₄·7H₂O, and 210 mg NaHCO₃ per liter.

B. Test Procedure:

1. Samples were to the nearest 0.1 mg. Then using ASTM D-1384 hardware,test bundles were prepared in the following sequence: teflon spacer,aluminum specimen, steel spacer, cast iron specimen, steel spacer,aluminum specimen, teflon spacer. A brass machine screw was insertedthrough the test fixture and the test bundle in order to secure thebundle to the fixture. The aluminum specimens in each bundle were of thesame alloy.

2. All bundles were prepared in this same sequence. The other bundleswere attached to the test fixture, making sure that there is at least 4inches between each bundle on the fixture.

3. The test fixture was placed in the flow loop and the connectionssecured to prevent leakage.

4. The test solution were heated to 88° C. (190° F.) and flow directthrough the flow loop.

5. The flow rate was adjusted to achieve the proper flow velocity acrossthe test fixture.

6. At the completion of the test, test fixtures were removed from flowloop.

7. The test bundles were dissembled and cleaned in accordance with ASTMD-1384. After drying the samples their weight was determined to thenearest 0.1 mg.

C. Calculations

Weight loss=A−B=C, where A=Weight before test, B=Weight after test, andC=Weight loss.

Due to the configuration of the individual test bundles, each alloy wasrun in duplicate. The individual weight losses for a single alloy agreedwithin 20%, and the average weight loss in milligrams was reported. (J.A. Worden, J. F. Burke & T. Cox, “Development of Aluminum Cooling SystemComponents for a 10.8 liter Diesel Engine”, SAE Technical Paper Series960643 pp. 46-59, 1996, incorporated herein by reference).

As can be seen from Table 1, the coolant composition containing adipicacid provides enhanced aluminum protection in the presence of hardwater. Further as can be observed for Examples 4 and 5, inclusion ofadipic acid in amounts as low as 0.2 wt % based upon the total weight ofthe coolant additive provides enhanced aluminum protection. FIGS. 1 and2 are scanned images of portions of two aluminum coupons that weresubjected to the Erosion Corrosion Test. Coupon 10 was immersed theExample 1 coolant formulation. Coupon 20 was immersed in the Example 3coolant formulation. It can be readily observed that coupon 20 hassignificantly more surface erosion than coupon 10. The original millingmarks can still be seen on coupon 10 as a series of substantiallyparallel lines or scratches extending across the width of the coupon.Conversely, coupon 20 is pitted, and the original milling marks areabsent. The surface of coupon 20 was eroded sufficiently to remove themilling marks.

Further, it is understood that the addition of adipic acidsynergistically enhances the protection of both aluminum and ironsurfaces in the presence of nitrite salts and molybdate salts. Inalternative embodiments, the addition of a combined organic acidcomponent that includes adipic acid and sebacic acid provides evenenhanced protection for the metal surfaces of the cooling system.

The present invention contemplates modifications as would occur to thoseskilled in the art. It is also contemplated that compositions andprocesses embodied in the present invention can be altered, rearranged,substituted, deleted, duplicated, combined, or added to other processesas would occur to those skilled in the art without departing from thespirit of the present invention. In addition, the various stages, steps,procedures, techniques, phases, and operations within these processesmay be altered, rearranged, substituted, deleted, duplicated, orcombined as would occur to those skilled in the art.

Further, any theory of operation, proof, or finding stated herein ismeant to further enhance understanding of the present invention and isnot intended to make the scope of the present invention dependent uponsuch theory, proof, or finding. While the invention has been illustratedand described in detail in the drawings, examples and foregoingdescription, the same is considered to be illustrative and notrestrictive in character, it is understood that only the preferredembodiments have been shown and described and that all changes andmodifications that come within the spirit of the invention are desiredto be protected.

1. An engine coolant composition comprising: an organic acid componentor salt thereof, said organic acid component comprising adipic acid andat least one of benzoic acid and a C₉-C₁₂ aliphatic dicarboxylic acid;an anticorrosion additive including molybdate, and at least one ofmercaptobenzothiazole, benzotriazole, tolyltriazole, nitrite, nitrate,and silicate; a buffer component comprising a sodium salt of at leastone of a borate salt or a phosphate salt and a freezing pointdepressant.
 2. The coolant composition of claim 1 wherein the adipicacid or a salt thereof is included in an amount between about 0.1 wt %and about 5 wt %, measured as the free acid and based on the totalweight of the coolant composition.
 3. The coolant composition of claim 1comprising between about 0.5 wt % and about 10 wt % of the organic acidcomponent, measured as the free acid and based upon the total weight ofthe coolant composition.
 4. The coolant composition of claim 1 whereinthe benzoic acid or C₉-C₁₂ aliphatic dicarboxylic acid is included in anamount between about 0.5 wt % and about 5 wt %, measured as the freeacid and based on the total weight of the coolant composition.
 5. Thecoolant composition of claim I provided to have a pH level between about7.5 and about 11 pH units.
 6. The coolant composition of claim 1provided as a liquid concentrate.
 7. The coolant composition of claim Iprovided as a ready-to-use-formulation for a internal combustion enginecooling system.
 8. The composition of claim 1 comprising: an organicacid component or salt thereof including adipic acid, benzoic acid andat least one C₉-C₁₂ aliphatic dicarboxylic acid; an anticorrosionadditive including molybdate, nitrite, nitrate, silicate and at leastone of mercaptobenzothiazole, benzotriazole, or tolyltriazole; a boratesalt; and a freezing point depressant.
 9. The composition of claim 1comprising: an organic acid component or salt thereof, said organic acidcomponent consisting of adipic acid, benzoic acid and at least oneC₉-C₁₂ aliphatic dicarboxylic acid; an anticorrosion additive includingmolybdate, nitrite, nitrate, and at least one of mercaptobenzothiazole,benzotriazole, or tolyltriazole; a phosphate salt; and a freezing pointdepressant.
 10. The composition of claim 1 comprising: between about 0.1wt % and about 0.5 wt % adipic acid, between about 1.0 wt % and about2.0 wt % of an aliphatic dicarboxylic acid or a salt thereof, saiddicarboxylic acid selected from the group consisting of: sebacic acid,dodecanedioic acid and mixtures thereof, between about 0 wt % and about0.5 wt % nitrite salts, between about 0 wt % and about 0.5 wt % nitratesalts, between about 0 wt % and about 0.5 wt % molybdate salts, betweenabout 0 wt % and about 0.5 wt % silicate salts, between about 0.1 wt %and about 0.5 wt % of at least one of mercaptobenzothiazole,benzotriazole, or tolyltriazole, and between 0.1 wt % and about 0.5 wt %of at least one of borate salts and phosphate salts; and between about80 wt % to about 99 wt % of at least one of ethylene glycol or propyleneglycol.
 11. A coolant composition comprising, in weight percent: betweenabout 0.1 wt % and about 0.5 wt % adipic acid, between about 1.0 wt %and about 2.0 wt % sebacic acid, between about 0.1 wt % and about 0.5 wt% of at least one of mercaptobenzothiazole, benzotriazole, ortolyltriazole, between about 80 wt % to about 99 wt % of at least one ofethylene glycol or propylene glycol, and optionally between about 0.1 wt% and about 0.5 wt % molybdate salts.
 12. The composition of claim 11consisting essentially of, in weight percent: between about 0.1 wt % andabout 0.5 wt % adipic acid, between about 2.0 wt % and about 3.0 wt % ofan aliphatic dicarboxylic acid pr a salt thereof, said dicarboxylic acidselected from the group consisting of: sebacic acid dodecanedioic acid,and a mixture thereof, between about 0.5 wt % and about 2.5 wt % benzoicacid, between about 0.1 wt % and about 0.5 wt % nitrite salts, betweenabout 0.1 wt % and about 0.5 wt % nitrate salts, between about 0.1 wt %and about 0.5 wt % molybdate salts, between about 0.1 wt % and about 0.5wt % of at least one of mercaptobenzothiazole, benzotriazole, ortolyltriazole, and between about 80 wt % to about 99 wt % of at leastone of ethylene glycol or propylene glycol.
 13. An engine coolantcomposition comprising: an organic acid component, said organic acidcomponent comprising adipic acid and at least one of benzoic acid and aC₉-C₁₂ aliphatic dicarboxylic acid or salts of these acids; ananticorrosion additive including molybdate, and at least one ofmercaptobenzothiazole, benzotriazole, tolyltriazole, nitrite, nitrate,and silicate; a buffer component comprising at least one of a boratesalt or a phosphate salt; and hard water.
 14. The coolant composition ofclaim 13 comprising a freezing point depressant.
 15. The coolantcomposition of claim 13 wherein the adipic acid or a salt thereof isincluded in an amount between about 0.1 wt % and about 5 wt %, measuredas the free acid and based on the total weight of the coolantcomposition.
 16. The coolant composition of claim 13 comprising betweenabout 0.5 wt % and about 10 wt % of the organic acid component, measuredas the free acid and based upon the total weight of the coolantcomposition.
 17. The coolant composition of claim 13 wherein the benzoicacid or C₉-C₁₂ aliphatic dicarboxylic acid or a salt thereof is includedin an amount between about 0.5 wt % and about 5 wt %, measured as thefree acid and based on the total weight of the coolant composition. 18.The coolant composition of claim 13 provided to have a pH level betweenabout 7.5 and about 11 pH units.
 19. A method of reducing the corrosionof metal surfaces in a cooling system having a recirculating liquidcoolant comprising hard water, said method comprising: adding to saidliquid coolant, an additive comprising an organic acid component or saltthereof, said acid component comprising a mixture of a C₄-C₆dicarboxylic acid and at least one of benzoic acid or a C₉-C₁₂ aliphaticdicarboxylic acid; and an anti-corrosion additive including molybdate,and at least compound selected from the group consisting of:mercaptobenzothiazole, benzotriazole, tolyltriazole, nitrite, nitrate,and silicate.
 20. The method of claim 19 wherein the liquid coolant ismaintained at a pH level between about 7.5 and about 11 pH units. 21.The method of claim 19 wherein the C₄-C₆ dicarboxylic acid or saltthereof is added in an amount sufficient to enhance the inhibition ofcorrosion of aluminum containing components relative to a liquid coolantwithout the C₄-C₆ dicarboxylic acid or salt thereof.
 22. The method ofclaim 19 wherein the additive comprising a buffer agent selected fromthe group consisting of: borates, phosphates, benzoates and mixturesthereof.